The present invention relates generally to the recovery of usable products from the pyrolysis of material containing hydrocarbons. More specifically, the present invention relates to the recovery of oil from the gas formed when scrap tires are pyrolysed.
As the supply of available landfill space decreases, environmentally sensitive disposal of consumed vehicle tires presents an ever increasing problem. In the United States alone, over 280,000,000 vehicle tires are scrapped and shipped to landfills each year. Although some of the used vehicle tires are recycled to be used in pavement and others are burned as boiler fuel, more than 80% of used vehicle tires end up being deposited in landfills. Discarding vehicle tires in landfills has been recognized as a significant waste of a recyclable resource. For many years, it has been known that used vehicle tires can be recycled by pyrolysis to obtain valuable by-products that can be sold and reused. Pyrolysis, generally speaking, is a thermal distillation or decomposition of a substance, especially one containing hydrocarbons. In the case of used vehicle tires, this process is carried out in the absence of oxygen and at temperatures generally between 500° C. and 800° C.
The process of decomposing used tires by pyrolysis allows the recovery of substantial amounts of oil, gas, carbon black and steel. Many different processes have been designed to recover these valuable products produced by pyrolysis, and the various techniques known for recovering these products each have their own unique and difficult problems. For example, the recovery of oil formed when scrap tires are pyrolysed has always been a challenge. Oil is typically produced by condensation of pyrolysis gas produced in the pyrolysis reactor, but these gases typically also include particulate matter, primarily carbon dust and glass fibers, which also are driven off from the scrap tires when pyrolysed. This particulate matter accumulates in fittings, vents and flame arresters, which eventually obstruct passages. In the past, particulate matter in the pyrolysis exhaust gas has been removed in a cyclone. However, if oil cools prematurely and begins to condense in the cyclone, the condensed oil will provide a surface for the particulate matter to adhere to. This not only may result in obstructions in the cyclone, but may also result in poor separation performance for the cyclone as it causes undesirable changes to inherent design parameters of the cyclone. In addition, if a packed bed condenser is employed in the system, particulate matter can foul the packing thus blocking off the open area and causing an intolerable rise in the pressure drop across the bed.
Another of the difficulties presented when recovering oil is caused by the fact that in addition to the oil vapors generated in the pyrolysis reactor, water vapor is also carried with the oil vapor. It is often the case with pyrolysis oil that it has a specific gravity close to that of water. As a result, if water and such oil are condensed together, they can form an emulsion that is difficult to separate.